No financial details were disclosed, but United said Mkhitaryan was joining as "part of the deal" to bring Sanchez to Old Trafford.

Signing Sanchez is being viewed as a real statement by United, like Eric Cantona joined in 1992 and Robin van Persie — who also arrived from Arsenal — in 2012. Beating City to the Chile forward will make his arrival all the more sweet for United fans and Mourinho.

"Alexis is one of the best attacking players in the world," Mourinho said. "He will bring his ambition, drive and personality, qualities that make a Manchester United player, and a player that makes the team stronger and the supporters proud of their club dimension and prestige."

City came close to signing Sanchez in August and looked to be the favorite to get him this month, only to end its interest in the forward following a rival bid from United. The Premier League leader said Sanchez and his agent increased their financial demands and that it didn't want to destabilize the team by bringing in a player who would be its highest earner.

City, the league leader by 12 points, didn't particularly need Sanchez, who had entered the final six months of his contract at Arsenal. That wasn't necessarily the case for United.

Sanchez will add some dynamism and unpredictability to a front line that already includes Romelu Lukaku, Anthony Martial and Marcus Rashford. Mourinho tried unsuccessfully to sign a winger in the last offseason.

Sanchez joined Arsenal from Barcelona in July 2014 for about 30 million pounds, choosing a move to London amid interest from Liverpool.

He was the top scorer in two of his three completed seasons at Emirates Stadium and helped Arsenal win the FA Cup in 2015 and '17, quickly becoming a favorite with the fans. However, with Sanchez happy to run down his contract, Wenger accepted the need to sell his star player.

Wenger rejected the theory that Sanchez was disrupting the harmony in the Arsenal team in his final months there.

"He's a very professional player who has been committed until the last minute," Wenger said. "In training, he was practicing with full power, so I never questioned that. I never had any doubts about that."

Before Arsenal, Sanchez scored 39 goals in his three seasons at Barcelona after joining from Italian club Udinese.

Mkhitaryan was substituted at halftime of his first league start for United, setting the tone for what has turned out to be a disappointing spell after arriving in English soccer for $33.5 million and with a big reputation in 2016.

Mkhitaryan moved to United from Borussia Dortmund, where he was the German league player of the year, but struggled to secure a regular place in the team under Mourinho except in the first few months of this season.

The Armenia international scored 23 goals and set up 32 more in his last season at Dortmund but failed to reproduce anything close to those numbers at United.

With injuries affecting Mkhitaryan in his early months at United, Mourinho said the player needed time to adjust to the physicality and intensity of the Premier League.

He finished last season by scoring an acrobatic goal in United's 2-0 win over Ajax in the Europa League final in Stockholm and began this season well, too, setting up five goals in his first three games.

Mkhitaryan has been a marginal figure at United in recent months, with Jesse Lingard starting ahead of him behind Lukaku. He has five goals in 39 league appearances for United, rarely completing 90 minutes.

The 29-year-old Mkhitaryan has previously said his favorite team was Arsenal and his impressive technique, allied with Wenger's naturally attacking philosophy, should make him a good fit at the London club.

"He creates chances, he defends well, he can absorb distances and he's very committed as well," Wenger said. "I must say he's a player who has all the attributes."

Sanchez's debut for United could come on Friday, in the FA Cup fourth-round match at fourth-tier Yeovil.

Mkhitaryan is cup-tied in that competition, so could make his debut against Swansea next week.